The present invention relates to a method of regulating a single sideband up converter of the type which includes two mixer stages and which is supplied with an oscillator signal having a preselected frequency and with an intermediate frequency signal that is to be converted, each mixer stage additionally receiving control signals to compensate for spurious signals of the mixer components. As used herein the term "spurious signals" includes one or more of the electrical changes which may occur due to component aging, stray capacitance or inductance resulting in frequency variations, temperature effects, and changes in oscillator signal level. The invention also relates to an arrangement for implementing the method.
In connection with single sideband up converters it is often necessary to suppress high interference, particularly in radio communications devices employing higher valued types of digital modulation, such as, for example, 64 QAM (quadrature amplitude modulation) and 256 QAM. In the past, the undesired sideband signal was filtered out by means of a multi-circuit bandpass filter tuned to the RF channel (see ANT Nachrichtentechnische Berichte [Communications Technology Reports issued by ANT], No. 2, December, 1985, page 27). Today, because of the use of single sideband mixers and control of oscillator suppression by way of PROMs and D/A converters (see U.S. Pat. No. 4,593,411) this is no longer necessary.